David Cameron responded in admirably robust fashion, by pointing out that Britain defeated fascism, abolished slavery and “invented most of the things worth inventing”. He might also have added that Britain’s economy is a third larger than Russia’s, so if no one listens to us, then the Kremlin really is in trouble.

But there is a serious point here. Economic strength underpins every other dimension of national power. When you have an economy as big as Britain’s – a GDP of about £1.5 trillion, the sixth biggest in the world – you can exert as much global influence as you’re prepared to pay for. The only question is whether you have the will.

At the moment, Britain chooses to spend 2 per cent of GDP on defence and 0.7 per cent on overseas aid. Throw in the comparatively tiny sums that we spend on the Foreign Office, the BBC World Service and the British Council and, when all is said and done, the British government spends rather less than 3 per cent of GDP on projecting the country’s power and influence around the world. Russia’s total defence spending, meanwhile, amounts to 5 per cent of GDP.

Government, in the end, is about priorities. Britain opts to spend 15 per cent of its national income on welfare benefits – or, in relative terms, five times more than we devote to our role in the world. Those priorities mean that we consciously choose to exert less global influence than we otherwise could in order to devote resources to our domestic problems.

That is an entirely legitimate choice. The point is that countries have more discretion than you might think. If you fall down the international pecking order, it’s probably because you chose that fate, not because you were forced into decline by a ruthless rival.

In the end, the question of whether Britain is a nation that shapes the world depends on the collective will of our political class. What I found most depressing about the Syria debate in parliament was the impression that many of our politicians no longer have that resolve.

Isolationism is hugely tempting, particularly in times of economic hardship. It’s always easy to argue that we should leave the world to take care of itself, choose the easy course, stay out of the most difficult international problems and contribute nothing except humanitarian aid and a modest amount of diplomacy. David Cameron and William Hague are honourable exceptions, but many British politicians of all parties appear to be succumbing to this tendency.

If Britain does tread the path of global retreat, we will indeed become an irrelevant island pretty quickly. Sadly, the Syria vote was a step in that direction. But no one will have forced this fate upon us. It would be our decision and, in my view, our tragic mistake.